Organic compounds -- part of the class 532-570 series – Organic compounds – Oxygen containing
Reexamination Certificate
1999-09-10
2001-11-20
Padmanabhan, Sreeni (Department: 1621)
Organic compounds -- part of the class 532-570 series
Organic compounds
Oxygen containing
C562S418000, C562S480000, C562S889000
Reexamination Certificate
active
06320083
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to the use of ionic liquids in the carbonylation of alkyl aromatic compounds to form the corresponding aromatic aldehyde.
2. Description of the Related Art
Carbonylation of an aromatic compound can be carried out by a reaction generally referred to as the Gatterman-Koch reaction. Published in 1897, Gatterman and Koch described the direct carbonylation of various aromatic compounds by the use of carbon monoxide and hydrogen chloride in the presence of aluminum chloride and cuprous chloride (Gatterman, L. and Koch, J. A., Chem. Ber., 30, 1622 (1897)). The reaction was subsequently expanded to include other Lewis acids. Further, it was discovered that the cuprous chloride could be eliminated if the CO pressure was increased. A review of such reactions is set forth in Olah, G. A., “Friedel-Crafts and Related Reactions”, Wiley-Interscience, N.Y., Vol. III, 1153 (1964).
U.S. Pat. No. 2,485,237, for example, describes replacing the hydrogen chloride and aluminum chloride catalyst combination with hydrogen fluoride and boron trifluoride. Further use of the HF-BF
3
catalyst is described in U.S. Pat. No. 3,284,508 where the recovery of the fluorides is stated to be improved.
Other catalysts that have been reported for use in a Gatterman-Koch type carbonylation reaction include combinations of Lewis and strong Bronsted acids such as SbF
5
-HF as is described in U.S. Pat. No. 4,218,403. The use of Bronsted superacids alone, such as fluorosulfonic acid or trifluoromethane sulfonic acid, were also reported to be effective catalysts. See for example Olah, G. A., Laali, K., and Farooq, O.,
J. Org. Chem.,
50, 1483 (1985).
These processes generally form an aldehyde-acid catalyst complex that must be dissociated in order to separate the aldehyde product. While the complex can be dissociated by known techniques such as the addition of water to the solution, these techniques may destroy or chemically alter the catalyst thereby making the reuse of the catalyst impossible, impractical, or expensive.
U.S. Pat. No. 4,554,383 recites the use of a “melt” catalyst of aluminum halide and alkyl pyridinium chloride in the selective carbonylation of toluene to tolualdehyde. The yields reported are generally 10% or less. Although not explicitly stated, it appears that the “melt” is what would today be called an ionic liquid. An ionic liquid is a liquid that is composed entirely of ions. Descriptions of ionic liquids can be found in Seddon, K. R.,
Molten Salt Forum
, 5-6, pp. 53-62 (1998) and Seddon, K. R.,
Kinetics and Catalysts
, 37, 5, pp. 743-748 (1996). In this patent, the ionic liquid is comprised of pyridinium
+
and AlCl
4
−
ions. Because equimolar amounts of aluminum halide and alkyl pyridinium chloride are combined in making this ionic liquid, the ionic liquid used in the examples is neutral; i.e., neither basic nor acidic.
It would be desirable to provide a process that obtains good conversion of alkyl aromatic compounds to the corresponding alkyl aromatic aldehyde. Further, it would be desirable to provide a process that allows for convenient separation of the aldehyde product from the reaction mixture.
SUMMARY OF THE INVENTION
The present invention relates to a process for carbonylating alkyl aromatic compounds, which comprises the step of reacting an alkyl aromatic compound with carbon monoxide in the presence of an acidic ionic liquid to form an alkyl aromatic aldehyde. The ionic liquid can be intrinsically acidic or it can be rendered acidic by the incorporation of acid. In a preferred embodiment, the ionic liquid is comprised of a quaternary nitrogen-containing cation and a metal halide anion, the anion being contained in the ionic liquid in a mole fraction greater than 0.5. Such an ionic liquid is intrinsically acidic. The alkyl aromatic compounds are typically toluene or xylene, although other aromatics are also suitable, which are converted to p-tolualdehyde and dimethyl benzaldehyde, respectively. The use of an ionic liquid can provide for more convenient separation of the aldehyde product and/or recycling of the acidic ionic liquid catalyst.
A further application of the invention is to subject the aldehydes thus formed to oxidation to produce an acid or anhydride. For example, p-tolualdehyde can be oxidized to terephthalic acid, a commonly used monomer in the production of commercial polyesters. Similarly, dimethyl benzaldehyde can be oxidized to obtain trimellitic anhydride. Thus, the present invention can also provide a convenient and economical route to the production of these and other valuable compounds.
DETAILED DESCRIPTION OF THE INVENTION
The present invention relates to the use of acidic ionic liquids as a catalyst in the carbonylation of alkyl aromatic compounds. An ionic liquid is a liquid that is made up of ions. Frequently the ionic liquid consists of organic cations and inorganic anions, although it is not limited thereto. The ionic liquid can have a high melting temperature such as in the case of the molten salt form of NaCl, but preferably has a melting point of less than 100° C., more preferably less than 50° C. For example, ionic liquids that are liquid at room temperature, i.e., melting at, or being liquid at, around 30° C. or less are preferable. In general, ionic liquids have low viscosity, essentially no vapor pressure, good heat transfer characteristics and are thermally stable.
The cations of the ionic liquid include organic and inorganic cations. Examples of cations include quaternary nitrogen-containing cations, phosphonium cations, and sulfonium cations. The quaternary nitrogen-containing cations are not particularly limited and embrace cyclic and aliphatic quaternary nitrogen-containing cations. Typically, the quaternary nitrogen-containing cation is an n-alkyl pyridinium, a dialkyl imidazolium, or an alkylamine of the formula R
4−X
NH
X
wherein X is 0-3 and each R is independently a C
1
to C
8
alkyl group. Preferred quaternary nitrogen-containing cations are represented by the following formulas I and II:
wherein R
1
-R
3
each independently represent a straight or branched chain alkyl group having 1 to 12 carbon atoms, generally 1-6 carbon atoms. R
1
is preferably a butyl group. R
2
and R
3
are preferably different groups, so as to make the cation asymmetrical, and typically contain 1 to 4 carbon atoms. It is believed that unsymmetrical cations can provide for lower melting temperatures.
The phosphonium cations include those of the formula R
4−X
PH
X
wherein X is 0-3 wherein each R group is an alkyl or aryl group such as an alkyl group having 1 to 8 carbon atoms or a phenyl group. The sulfonium cations include those of the formula R
4−X
SH
X
wherein each R group is an alkyl or aryl group such as an alkyl group having 1 to 8 carbon atoms or a phenyl group.
Examples of particularly preferred cations are N-butylpyridinium, 1-ethyl-3-methylimidazolium (hereinafter sometimes referred to as “[emim]”), and 1-butyl-3-methylimidazolium, the structures of the former two compounds being set forth below:
The cation present in the ionic liquid can be a single species or a plurality of different species. Both of these embodiments are intended to be embraced, unless otherwise specified, by the use of the singular expression “cation.”
The anion used in the ionic liquid is not particularly limited and includes organic and inorganic anions. Generally the anion is derived from an acid, especially a Lewis acid. The anions are typically metal halides as described in more detail below, boron or phosphorus fluorides, alkylsulfonates including fluorinated alkyl sulfonates such as nonafluorobutanesulfonate, and carboxylic acid anions such as trifluoroacetate and heptafluorobutanoate. The ionic liquid can be composed of one or more species of anion. In this regard, the use of the singular term “anion” is intended to cover both single species and multiple species embodiments, unless otherwise noted or apparent from the context. Specific examples o
ExxonMobil Chemical Co.
Moreno Louis N.
Padmanabhan Sreeni
LandOfFree
Process for making aromatic aldehydes using ionic liquids does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Process for making aromatic aldehydes using ionic liquids, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Process for making aromatic aldehydes using ionic liquids will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2614385